BER Analysis of Wideband Code Division Multiple Access

Transcription

1 International Journal of Electronics and Computer Science Engineering 115 Available Online at ISSN BER Analysis of Wideband Code Division Multiple Access Veeranna.D 1, Sanjeev Kumar Sharma 2, Yashwant Singh 3 1 Asst. Professor, Electronics & Communication Engineering Dept, Lingaya s University, Faridabad 2 M.Tech student, Lingaya,s university, Faridabad 3 Lecturer, Marathwada Institute of Technology,Bulandshahr 1 veera.daravath@gmail.com 2 sanjeevhi2007@gmail.com Abstract There has been a dramatic change in the field of field of telelcommunication service. M-ary Quadrature Amplitude modulation and Quadrature Phase shift Keying (QPSK) modulation schemes are considered in Wideband code Division Multiple Access(WCDMA) system. Here we are using MATLAB for simulation and evaluation of BER ( Bit Error Rate )and SNR(Siganl to Noise Ratio). There is analysis of Quadrature Phase shift Keying and 16 ary Quadrature Amplitude modulation which are being used in WCDMA (wideband code division multiple access) system. This system is more suitable modulation technique to suit the channel quality Keywords Bit Error Rate, Code Division Multiple Access, Quadrature phase shift keying, and Quadrature Amplitude modulation I. INTRODUCTION WCDMA also known as third generation system Universal Mobile Telecommunication System (UMTS) uses Wideband Code Division Multiple Access (WCDMA) for 3rd generation cellular Communication System. WCDMA contain air interfaces for the third generation of wireless communications developed within the framework of the International Mobile Telecommunications (IMT)-2000, as defined by the International Telecommunication Union (ITU). The systems are designed for multimedia communication can be enhanced with high quality images and video and access to information and services on public and private networks will be enhanced by the higher data rates and new flexible communication capabilities of third generation systems. High data rate signal transmission can be transmitted over the air by using W-CDMA system, thus enabling of multimedia rich applications such as video streams and high resolution pictures to end users. Thus, we need suitable modulation technique and error correction mechanism to be used in W-CDMA system. In 2G networks, Gaussian Minimum Shift Keying (GMSK) modulation scheme is widely used in GSM (Global System for Mobile) Communication.1 bit per symbol data is transmitted in this modulation scheme. so we can see that GMSK is not suitable for mobile communication. It is requirement to study the performance of new modulation technique that deliver high data rate effectively in multipath fading channel. WCDMA cellular communication require perfect modulators demodulators filter and transmission path for implementation of high data rate modulation technique.error is introduced by noise and interference in the channel for more bit per sample in modulation scheme. II. NOISE AND INTERFERENCE AND INTERFERENCE A. Additive White Gaussian Noise (AWGN) For ideal communication system, the channel is anticipated only with additive white Gaussian noise where it is free from intersymbol interference (ISI). This is usually a good starting point for understanding basic performance relationships. The primary source of performance degradation is thermal noise generated in the receiver. Often, external interference received by the antenna is more significant than thermal noise. The term additive means the noise is superimposed or added to the signal that tends to obscure or mask the signal where it will limit the receiver ability to make correct symbol decisions and limit the rate of information transmission. Thus, AWGN is the effect of thermal noise generated by thermal motion of electron in all dissipative electrical components i.e. resistors, wires and so on [1].

2 IJECSE,Volume1,Number 1 Veeranna.D et al 116 Mathematically, thermal noise is described by a zero-mean Gaussian random process where the random signal is a sum of Gaussian noise random variable and a dc signal that is z = a +n (2) (1) Where pdf for Gaussian noise can be represented as follows where is the variance of n. (2) A simple model for thermal noise assumes that its power spectral density Gn(f) is a flat for all frequencies and is denoted as Where the factor of 2 is included to indicate that Gn(f) is a two-sided power spectral density. When noise power has such a uniform spectral density, it is referred as white noise. The adjective "white" is used in the same sense as it is with white light, which contains equal amounts of all frequencies within the visible band of electromagnetic (EM) radiation. Since thermal noise is present in all communication systems and is a prominent noise source for most system, the thermal noise characteristics that are additive, white and Gaussian are most often used to model the noise in communication systems. (3) B. Rayleigh Fading In a wireless mobile communication system, a signal can travel from transmitter to receiver over multiple reflective paths; this phenomenon is referred to as multipath propagation. The effect can cause fluctuations in the received signal s amplitude, phase, and angle of arrival, giving rise to the terminology multipath fading. The end-to-end modeling and design of systems that mitigate the effects of fading are usually more challenging than those whose sole source of performance degradation is AWGN. Generally, fading effects in mobile communication can be categorized as large scale fading and small scale fading. Large scale fading represents the average signal power attenuations or path loss due to motion over large areas. This phenomenon is affected by prominent terrain such as hills, forests, building and others. The receiver is often being shadowed by such prominences. On the other hand, small scale fading refers to dramatic changes in signal amplitude and phase that can be experienced as a result of small changes (as small as a half-wavelength) in the spatial separation between a receiver and transmitter [13]. Small scale fading is also called Rayleigh fading because the envelope of the received signal is described by a Rayleigh pdf. The received signal consists of large number of multiple reflective paths and there is no line-of-sight signal component. When there is a dominant non-fading signal component present, such as a line-of-sight propagation path, the small-scale fading envelope is described by a Rician pdf..

3 BER Analysis of Wideband Code Division Multiple Access C. Doppler Shift Doppler shift is categorized as time variance in frequency domain of small scale fading. Referring to Doppler power spectral density, S(v) plotted as a function of Doppler frequency shift, v. For the case of the dense-scatterer model, a vertical receive antenna with constant azimuthal gain, a uniform distribution of signals arriving at all angles through the range (0,2π) and an unmodulated continuous wave (CW) signal, the signal spectrum at the antenna terminal is (4) where fd is Doppler spread. Doppler shift produced by a vehicular antenna traveling among the stationary scatterers of the dense scattered model. The largest magnitude (infinite) of S(v) occurs when the scatterer is directly ahead of the moving antenna platform or directly behind it. Doppler power spectrum is referred to as the spectral broadening or Doppler spread, denoted by fd, and sometimes called the fading bandwidth of the channel. Equation describes the Doppler frequency shift. In a typical multipath environment, the received signal arrives from several reflected paths with different path distances and different angles of arrival, and the Doppler shift of each arriving path is generally different from that of another path. Therefore, the effect on the received signal is seen as a Doppler spreading. III. SIMULATION METHODOLOGY This paper is based on simulation. Thus, MATLAB has been identified to simulate the WCDMA systems based on related theories and parameters. The simulation is done based on single user in the WCDMA system and using Simulink Block Set as the base for system development. The WCDMA system with two different channel conditions which may or may not includes channel coding. The system which has been specified for the simulation purposes are as follows: 1. WCDMA system in AWGN channel without convolutional coding. 2. WCDMA system in AWGN channel with convolutional coding. 3. WCDMA system in AWGN and Rayleigh Fading channel without convolutional coding. 4. WCDMA system in AWGN and Rayleigh Fading channel with convolutional coding.

4 IJECSE,Volume1,Number 1 Veeranna.D et al 118 Figure.1 Flowchat for WCDMA system model is used in simulink and M-file. The simulation is followed by using m file. In this approach, the simulation is successfully done using QPSK modulation technique IV. RESULTS AND DISCUSSION A. Results for AWGN channel The following depicted results obtained from simulation. For better illustration, Figure shows bit error rate (BER) combination of AWGN channel with and without convolution coding.

5 BER Analysis of Wideband Code Division Multiple Access Figure.2 BER of AWGN with and without convolutional coding B. Results for AWGN and Multipath Rayleigh Fading in communication Channel Figure.3 BER of AWGN and multipath Reyleigh Fading with Doppler shift =55.56 Hz It is proposed that Rician fading is included in the channel in addition of AWGN and multipath Rayleigh fading channel. Then, comparison can be made between these channels. It is also proposed that implementation of interleaver in the system in order to overcome the problem of irreducible error rate.

6 IJECSE,Volume1,Number 1 Veeranna.D et al 120 REFERENCES [1] J. M. Holtzman, A Simple, Accurate Method to Calculate Spread-Spectrum Multiple- Access Error Probabilities, IEEE Trans. Communication, vol. 40, pp , Mar [2] Victor Wen-Kai Cheng, Wayne E. Stark, Adaptive Coding and Modulation for Spread Spectrum, IEEE Journal, [3] Troels E. Kolding, Frank Frederiksen, Preben E. Mogensen, Performance Aspects of WCDMA Systems with High Speed Downlink Packet Access (HSDPA), Nokia Network R&D, Denmark, 2003 [4] Crovella, M.E., Bestavros, A., Self-Similarity in World Wide Web Traffic: Evidence and Possible Causes, IEEE/ACM Trans. on Networking, Vol. 5, No. 6, pp , December, [5] Y.Rosmansyah, P. Sweeney, R. Tafazolli, Air- Interface Techniques for Achieving High Data Rates for UMTS, IEEE 3G Mobile Communication Technologies, Conference Publication No. 477, pp , March [6] [Azlin BT Mohd Fahmi Performance Study On Effect Of Convolutional Coding In WCDMA system With Different Channel Condtion University Teknologi Malasita,2005 [7] M. A. Masud, M. Samsuzzaman, M. A.Rahman, Bit Error Rate Performance Analysis on Modulation Techniques of Wideband Code Division Multiple Access, JOURNAL OF TELECOMMUNICATIONS, VOLUME 1, ISSUE 2, MARCH 2010